Add pagination to comments to prevent browser crash

Summary

Closes #720 (closed) - Fix browser crash with 1000+ comments

Changes

• Limit initial render to 50 root-level comments (prevents browser crash)
• Add "Show more comments" button for loading additional comments
• Add visible pagination links for crawler accessibility (?comments_page=2&sort=trending#comments)
• Create /api/comments/[author]/[permlink] route with in-memory caching (60s TTL)
• Support URL-based navigation for bookmarkable/shareable comment pages

How It Works

1. Browser users: Click "Show more" for smooth loading (no page reload)
2. Crawlers: Follow visible <a href> links to discover all comments
3. Direct URLs: ?comments_page=2 loads page 2 directly via SSR

Testing

• Open https://blog.openhive.network/hive-125125/@ecency.waves/waves-20251102jlybmw (1962 comments)
• Verify page loads without "Aw, Snap!" crash
• Verify "Show more comments" button works
• Verify pagination link appears below button
• Test ?comments_page=2 loads page 2 directly
• Test normal posts (no regression)

API Investigation

Tested Hive APIs for native pagination - none available on public nodes:

• database_api.list_comments - NOT available
• get_content_replies - times out on large posts
• bridge.get_discussion - works but returns all comments

Solution: Fetch all via get_discussion, cache on server, return paginated slices.